<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <style>
            .testColor{
                color: red;
            }
            #hehe{
                color: blue;
            }
            div span{
                color: palevioletred;
            }
        </style>
    </head>
   <body>
    <p>段落1</p>
    <p class="testColor">段落2</p>
    <p id="hehe">段落3</p>
<button class="testColor">按钮</button>
<span>外面的span</span>
<div >
    <span> 嵌套span</span>
</div>
   </body>
</html>